cfg80211: Ingore country IEs with a zero set of number of channels

Previous to this and the last patch, titled,

"cfg80211: Fix 2 GHz subband calculation for country IEs"

we would end up treating these IEs as single channel units. These are in
fact just bogus IE triplets so ignore the entire IE if these are found.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>